This invention relates to charge transfer devices and, in particular, to such devices which include means for moving charge in two noncollinear directions in the major plane of the device.
"Charge Transfer Device" (CTD) is by now the well-known generic description for devices which store and transfer charge carriers in a storage medium by means of appropriate potentials applied to series of electrodes disposed upon an insulating layer overlying one surface of the medium. These devices may be of the charge coupled (CCD) or bucket brigade (BBD) type. In the basic bucket brigade device, regions of fixed charge are provided in the storage medium beneath each electrode and extending slightly into the area below an adjacent electrode in the charge transfer path. When an electrode is pulsed, the region of charge immediately under it is reverse-biased and the channel between this region and its neighbor is inverted to permit the transfer of charge. Thus, mobile charge carriers are stored in fixed charge regions as majority carriers and transferred through the channels as minority carriers. The basic charge coupled device stores charge carriers under depletion biased electrodes and transfers the charge carriers by creating a succession of potential wells at the storage medium surface along the transfer path. Charge is therefore stored and transferred in the form of discrete packets of minority carriers in the medium.
Various electrode configurations have been proposed for moving the charge carriers in essentially a linear path. These include schemes for moving the charge in serpentine fashion and for reversing the transfer to the opposite direction. In many information processing applications, such as time division multiplexing and circulating memories, it is necessary to provide for conversion from serial to parallel and from parallel to serial transfer of charge in the device as well as a number of other logic operations. This versatility in operation generally requires the ability to transfer charge from any particular storage location in either of two noncollinear directions. Prior art charge transfer devices have not provided this extra degree of freedom fully in the transfer process. In the frame transfer and store imaging device, for example, parallel to serial conversion is accomplished at one end of the electrode array (see, U.S. patent application of M. Tompsett, Ser. No. 285,054, filed Aug. 30, 1972). Such a device is limited to a single mode and cannot perform logic operations necessary for other applications, such as serial to parallel conversion.
It is therefore the primary object of the present invention to provide a charge transfer device which will readily permit transfer of charge in at least two noncollinear directions in order to perform the myriad logic operations required for present data needs.